Coating composition and coated tire

ABSTRACT

A composition comprised of polyvinylalcohol coating and at least one water insoluble particulate organic or inorganic material having a plate-like structure. Preferred particulate materials are flake mica and flake glass. In addition, there is provided a coated rubber tire having at least one of its surfaces coated with such composition.

This is a division of application Ser. No. 07/322,752 filed on Mar. 13,1989, now U.S. Pat. No. 4,911,218.

FIELD

This invention relates to a coating composition for various substratesand to a substrate coated with such composition. More particularly, itrelates to a coating composition for a cured rubber substrate and tosuch a coated cured rubber substrate. More specifically, the inventionrelates to a protective coating composition for a rubber tire sidewalland, a tire having a sidewall with such coating thereon.

BACKGROUND

Tire sidewalls are often coated with protective paints or coatings,particularly tire sidewalls having a color which contrasts with thetypical black colored remainder of the tire. The general purpose of sucha protective coat or paint is to inhibit or prevent migration ofchemicals to the tire rubber composition from the surface of an adjacentblack colored tire which would otherwise tend to stain and thus,discolor the rubber. The staining usually becomes evident after exposureof the contacted rubber surface to ultraviolet light such as sunlight.Such contact staining phenomenon is well known.

Rubber tires are typically black in color due to the carbon blackreinforcement contained therein. If a contrasting or other color isdesired for a part of the tire, then the carbon black is deletedtherefrom and a coloring pigment used. Conventionally, various of thecompounding ingredients used in the formulation of rubber for themanufacture of rubber products such as tires are of the staining type,namely, amine based antidegradants and aromatic rubber processing oils.Such materials tend to migrate to the surface of the rubber and maystain or discolor a rubber surface of another rubber article which maycome in contact with it for a period of time, particularly after thecontacted rubber is exposed to ultraviolet light.

Often, a polyvinylalcohol (PVA) based coating is used to protect suchcontrastingly colored rubber surfaces from other rubber surfaces of thestaining type because the polyvinylalcohol itself tends to be a barrierfor the migration of such staining material. Moreover, the PVA cannormally be easily removed from the coated rubber surface, when and ifdesired, by simple water washing, usually with a soap solution, sincethe PVA itself normally has a relatively high degree of watersolubility, particularly when the water contains a surfactant. Thus, thePVA coat is typically used for storage and shipping conditions and isusually removed by water washing by the user. Such use is well known.

PVA is normally used in conjunction with (mixed with) a plasticizertherefor so that the resulting PVA-based coating has a degree offlexibility. Such PVA mixture is referred to herein as PVA coating.

Tires are often stored under varying circumstances for various purposesso that they may be in contact with each other for a period of time suchas, for example, storage during their shipping or transportation tovarious locations and warehouse storing. The storage conditions can varyconsiderably and, sometimes, the tires are stored under relatively highhumidity conditions and sometimes at elevated temperatures.

Under such circumstances, where the tire surface has a PVA-based coatingthereon, it has been observed that under relatively high humidityconditions the PVA based coating softens and easily scuffs or abradesaway, particularly as one tire may rub against another during shipment,thereby leaving a portion of the contrastingly colored sidewallunprotected and susceptible to chemical contact migrating staining fromother adjacent and contacting rubber products, including tires.

At elevated temperatures, the aforesaid staining ingredients have agreater tendency to migrate to the surface of its host cured rubberproduct and, consequently, contribute to the staining of an adjacent andcontacting rubber surface which is contrastingly light colored--eventhrough many conventional (including polyvinyl alcohol) protectivebarrier coatings.

Accordingly, it is desired to provide a coating composition and aresultant coated rubber product, particularly a coated tire sidewallrubber surface, which will retard, inhibit and/or prevent the migrationof amine based antidegradants and aromatic rubber processing oils ontothe rubber sidewall surface, such as a white sidewall, from an adjacentand contacting black rubber surface.

DISCLOSURE AND PRACTICE OF THE INVENTION

In accordance with this invention, composition is comprised ofpolyvinylalcohol (PVA) coating, and at least one water insolubleparticulate organic and/or inorganic material, preferably an inorganicmaterial, having a plate-like structure in a weight ratio of suchparticulate material to the PVA in the coating (the PVA resin itself) inthe range of about 1/6 to about 1/1.

In further accordance with this invention, a coating composition iscomprised of polyvinylalcohol coating and about 16 to about 100 parts byweight of at least one plate-like structured material selected from micaand flake glass in a weight ratio of flake mica and/or flake glass basedon the PVA of said coating.

Preferably, the mica and/or flake glass has a particle size in the rangeof about one to about 300 microns, more preferably about 1 to about 50microns. A fine particle size is desired to enhance sprayability of thewater-based coating composition.

The plate-like structured material is of such materials having twosubstantially parallel opposing plate-like surfaces with an averagewidth to thickness ratio being in the range of about 5/1 to about 30/1.Typically, an average thickness is about 1 to about 2 microns.

In the practice of this invention, it is understood that the PVA coatingincludes a suitable plasticizer for the PVA, such as for example,glycerin and/or polyglycerol is typically used with the PVA in order tomake the PVA more flexible. While the choice of plasticizers may not beentirely critical, it should be a plasticizer which does notsubstantially degrade the resistance of the PVA to the migration of theaforesaid staining materials. For such purposes, glycerin and/orpolyglycerol are often used. However, if desired, the plasticizer caninclude a small amount of polyalkylenetherglycol, preferably apolyethylenetherglycol, with the amount used being commensurate withstain retardance desired. Such materials are relatively well known bythose having skill in such art for such purpose. Typically the PVAcoating is comprised of 100 parts by weight PVA and about 10 to about 20and up to about 30 parts by weight plasticizer. Such coating compositionis relatively well known to those skilled in such art.

As hereinbefore referenced, various ingredients are conventionally usedin the compounding of rubber for the manufacture of rubber articles,including tires, which are well known to those having skill in such artsuch as the various antidegradants, processing oils and the like.

The substantial addition of the flake mica with its plate-like structureto the PVA composition, although the mechanism may not be entirelyunderstood, has been observed to be particularly beneficial apparentlybecause its plate-like structure (with overlapping plates) reduces thepermeability of the "staining" ingredients and, thus, enhances thePVA-based coating. It has also been observed to apparently reduce thehydrophilicity of the PVA-based coating and, thus, helps to improve itsresistance to degradation upon exposure to high humidity conditions.

The flake glass with its plate-like structure has been observed toprovide similar results.

In further accordance with this invention, a pneumatic tire is providedhaving the coating of this invention on at least one of its sidewalls.

Indeed, there is a particular benefit in utilizing the coatingcomposition for coating at least one of the sidewalls of a rubber tire,particularly a pneumatic rubber tire, namely, to provide an enhancedresistance to contact-staining and a humidity resistant coating.

Thus, in accordance with this invention, a cured rubber tire is providedhaving at least one of its surfaces coated with the composition of thisinvention.

In further accordance with this invention, a pneumatic rubber tire isprovided having at least one portion thereof composed of a cured rubbercontaining a coloring pigment selected from at least one of titaniumdioxide and zinc oxide in the absence of carbon black where the surfaceof said portion has a coat thereon of the composition of this invention.

The polyvinylalcohol can generally be described as being about an 80 to99.5 percent hydrolyzed polyvinylacetate. Thus the PVA, as it would beunderstood by those having skill in the art, contains a small amount ofpolyvinyl acetate, although it is still conventionally referred to (asit is here) as polyvinylalcohol or PVA (rather than PVAC). It usuallyhas a number average molecular weight in the range of about 22,000 toabout 50,000 and a molecular weight average in the range of about 84,000to about 110,000, although these values are not considered critical butare desirable. Sometimes a molecular weight in the lower range is usedfor the PVA if a more flexible or pliable coating is desired.

The advantages of this invention are more particularly shown by thefollowing example in which the parts and percentages are by weightunless otherwise indicated.

EXAMPLE I

Sulfur cured rubber samples were obtained having the dimensions of about1 inch by 2 inches with a thickness of about 1/4 inch.

Both samples contained a particulate titanium dioxide white coloredpigment without carbon black reinforcement and thus were white in color.

Water based coating compositions were prepared as a mixture ofpolyvinylalcohol and plasticizer (Control Coating A) and as a mixture ofpolyvinylalcohol, plasticizer and flake mica (Experimental Coating B)and of polyvinylalcohol, plasticizer and flake glass (ExperimentalCoating C).

The water based coating compositions were individually coated onto thesurface of the white cured rubber samples to a wet thickness of 2 to 3mils and allowed to dry in a hot air circulating oven at a temperatureof about 120° to 140° C. Alternatively, the coatings could have beenallowed to dry at room temperature (about 20° C).

For illustrative purposes, the coating composition (A), as a Control,was comprised of a mixture as shown in Table 1. Coating composition (B),was of the same recipe as (A) except that it contained 5.2 parts flakemica and Coating Composition C was of the same recipe as (A) except thatit contained 5.2 parts of flake glass.

                  TABLE 1                                                         ______________________________________                                                       Parts                                                          Material       Coating A                                                      ______________________________________                                        Water          71                                                             PVA.sup.1      12.2                                                           Polyglycerol.sup.2                                                                           0.3                                                            Glycerine.sup.3                                                                              2.8                                                            Surfactant.sup.4                                                                             0.1                                                            Biocide        0.1                                                            Blue Dye       1.0                                                            Defoamer.sup.5 0.2                                                            ______________________________________                                         .sup.1 A polyvinylalcohol from Air Products Company obtained as Vinol 205     .sup.2 A polyglycerol from Chemical Components Inc. obtained as RZN.          .sup.3 Glycerin from P&G, Inc.                                                .sup.4 A fluorosurfactant from DuPont de Nemours & Co. obtained as Zonyl      FSP.                                                                          .sup.5 From Versa Chemical Co. identified as a paraffinic oilbased            material.                                                                

The flake mica was obtained from C. P. Hall, Inc. and reportedly had aless than about a 325 mesh size.

The flake glass was obtained as Flake Glass Type C from Owens-CorningFiberglas Corp. having a size passing through a 1/64 inch screen and ofa 1-2 micron thickness.

The coated rubber samples (A, B and C) were placed on a suitablesubstrate and a carbon black reinforced black colored cured rubber wasplaced on top of each of the coated samples. An approximately five (5)pound weight was placed on top of each of such assemblies.

The weighted assemblies were placed in a hot air circulating oven atabout 70° C. for about twenty-four (24) hours.

The assemblies were removed from the oven, disassembled and the samplesA, B and C washed with water to remove the aforesaid coatings therefrom.All samples looked white at this stage.

The cleaned samples were placed under U.V. (ultraviolet) lamps for abouttwo (2) hours.

The samples were visually inspected and also tested with a photovoltmeter (which measures surface reflectivity--an extent of whiteness inthis example).

The following results shown in Table 2 were observed.

                  TABLE 2                                                         ______________________________________                                                  Control A Samples B and C                                           ______________________________________                                        Observation:                                                                              slight staining,                                                                          remained white                                                    brownish tint                                                     ______________________________________                                    

An additional similar experiment was conducted by mixing 100 parts of aPVA based coating (approximately 68 parts water, 20-25 parts PVA andremainder primarily of flake mica with a control having no mica. Themixtures were sprayed onto the cured white colored rubber sample to wetthickness of about 2-3 mils and then dried, contacted with black curedrubber containing staining chemicals, similarly aged in an oven fortwenty-four (24) hours at 70° C. and then washed (to remove the coating)and exposed to ultraviolet light for about two (2) hours. Theirreflectivity was measured and the following values obtained as shown inTable 3.

                  TABLE 3                                                         ______________________________________                                                   Parts Flake Mica                                                                Control  D         E   F                                         Sample:      0        5         10  15                                        ______________________________________                                        Reflectivity 42       42        63  58                                        Rating                                                                        ______________________________________                                    

What is claimed is:
 1. A coating composition comprised of 100 parts byweight polyvinylalcohol and about 10 to about 30 parts by weight of atleast one of glycerin and polyglycerol and at least one water insolubleparticulate material having a plate-like structure selected from atleast one of flake mica and flake glass in a weight ratio of saidparticulate material to the PVA in the coating composition in the rangeof about 1/6 to about 1/1.
 2. The composition of claim 1 where saidplate-like structed material is an inorganic material having twosubstantially parallel opposing plate-like surfaces with an averagewidth to thickness ratio in the range of about 5/1 to 30/1.